Techniques to produce useful compounds through microbial metabolism (fermentation techniques in a broad sense) have been developed and used practically. For example, fungi of the genus Mortierella (e.g., Mortierella alpina) are known to produce polyunsaturated fatty acids (PUFAs) including arachidonic acid and are fungi particularly useful for industrial purposes (Patent Document 1).
For use of these fungi, breeding has been conducted, i.e., modifications have been made to improve the genetic traits of useful organisms (variety improvement). Particularly in fermentation techniques, breeding becomes very important in terms of improving the efficiency of microbial production of useful compounds and reducing the production costs of these compounds, etc.
To breed useful organisms having more desirable traits, transformation-based techniques are used. In this case, a DNA fragment encoding a protein necessary to acquire a desired trait is made expressible under the control of an appropriate gene promoter and then introduced into a useful organism to be bred (i.e., a host) to obtain a population of transformants. From among this population, a desired variety (strain) will then be selected. This procedure requires a gene promoter which is appropriate for the type of organism serving as a host or appropriate for the trait to be modified.
As to the transformation of filamentous fungi to which fungi of the genus Mortierella belong, many techniques have been reported. Moreover, in relation to the lipid production ability of fungi of the genus Mortierella, many enzyme genes involved in lipid synthesis systems have been obtained. However, there have been few reports about gene promoters required to introduce these useful enzyme genes into fungi of the genus Mortierella and to cause their expression at high levels.